[RJohnston]

Originally Posted by rainer

Thank you for that. I have saved it and will read it later. I did add a link on one of my posts.
Have a look and tell me what you think? Cheers" Ray
http://www.dpiphoto.eu/dpi.htm

To confuse the issue even more, he has errors in his article, he needs to proofread the content.

" From the moment you are going to print there is the matter of size, given in inches or centimeters. Only then you can speak of pixels per inch (ppi, regrettably ususally called dpi)."

In the computer if you change Pixels per inch from 300 to 1200 pixels per inch, you will see the SIZE of the file grow dramatically. So PPI does have a lot to do with a file on the computer. If you changed it to 72 per inch, it reduces the file dramatically in the computer. It appears even he is still confused about the relationship.

You can always speak of pixels per inch in a file, that is where they are relevant.... If you look at a file in Photoshop, directly from your camera, depending on the camera it will vary in PPI. He mentions DPI in Photoshop, I can not find anywhere in Photoshop where it mentions DPI.... ONLY when you get to setup PRINTING software or printer controls do you see a mention of DPI. Which as it should be, I never print lower than 600 DPI and many times set it higher.

Lets say a phone camera produces images at 50 or 72 PPI and a Nikon D200 (My current camera) produces 300 PPI in a raw file.that resolution is specified by NIKON as a resolution unit of 1 inch or 300 Pixels Per Inch... That gives the D200 much better resolution than a phone camera... I believe Nikon would be more correct, they made the camera. So in Photography is always spoken of as Pixels per inch in a photograph and Printers speak of resolution on paper as Dots Per Inch in a printer software...

You _never_ print pixels on a printer they only print dots which [u]represent the pixels.]/u]

DOTS PER INCH, has no bearing upon the number of pixels per inch, they are both different measurements, used for different reasons...... Originally computer printers printed mechanically with rods hitting the paper. They printed "dots" on the paper to make up an image. Then, they switched to different heads which "spray" DOTS on the paper instead, but all printers put DOTS on the paper..

If you look at an image printed at 100 dots per inch under a magnifying glass you coud actually count the number of dots and you see them as round dots on paper not square as pixels would be. If printed at 300, it would be more difficult to see. If printed at 1200 or 4800 dots per inch, then they blend more and you would need a microscope to see them.

It takes many DOTS to equal one Pixel in the image, horrizontally and vertically.
You can set the file in Photoshop to PPI to 300 to give good resolution. BUT, if you have the printer set to "spray" only 72 dots per inch the image will look weak or faded. Set the printer to 300 dots per inch (in the printer) and you get stronger or more saturated colors. Set the printer to 1200 DOTS per inch and you get very saturated colors on the print. When you view images on the screen, we see them with light behind them. On a print they are seen with reflected light so the greater number of DOTS per inch, the brighter they look. My printer can be set to 4800 dots per inch...

He may have written the article from memory. When writing, I recheck my facts in documentation for the Computer, Photoshop, my Nikon, and anything else I feel is relevant. He has other errors in the article also.
Not all articles you find on the Internet are accurate as you found.